Impact of long-term tillage management on utilization of microbial carbon sources in rhizosphere and non-rhizosphere soils under a double-cropping rice paddy field

In order to reveal the mechanism of microbial carbon (C) sequestration in paddy soil under different tillage management and to provide an important theoretical basis for perfecting the mechanism of C sequestration in paddy soil. C can indicate changes of soil nutrient content and soil microbial community, but more research is needed to study how C sources utilization characteristics respond to different tillage management under a double-cropping rice (Oryza sativa L.) paddy field in southern China. Hence, the impact of long-term (2005–2018) tillage management on utilization of microbial carbon sources in rhizosphere and non-rhizosphere soils under a double-cropping rice paddy field was studied by using ¹⁸O–H₂O method in this study. The tillage treatments were included: (1) moldboard plow with all crop residue removed as a control (CT), (2) moldboard plow with all crop residue incorporated (CTS), (3) no-tillage with all crop residue retained on the soil surface (NTS), and (4) rotary tillage with all crop residue incorporated (RTS). The results indicated that Richness, Shannon, and McIntosh indices were increased by application of crop residue management, compared with treatment without crop residue, and soil microbial growth rate, soil microbial biomass C content, and soil microbial basal respiration with CT treatment were significantly lower (p < 0.05) than that of NTS, RTS, and CTS treatments. And the soil C utilization efficiency in rhizosphere soil with NTS, RTS, and CTS treatments was significantly lower (p < 0.05) than that of CT treatment. Compared with CT and CTS treatments, the metabolic capacity of soil microorganisms to exogenous C sources with NTS and RTS treatments was increased, and the different types of exogenous C sources were showed as following: complex compounds < carbohydrate < amino acid < carboxylic acids. The redundancy analysis results showed that utilization characteristics of soil microorganisms to exogenous C sources were significantly changed under tillage and crop residue incorporated conditions. Hence, this result indicated that characteristics of soil C sources utilization were significantly increased combined applied with tillage and crop residue incorporated management.